1. Field of the Invention
The present invention concerns automatic transmission devices for automotive vehicles.
2. Background Art
In conventional automatic transmissions, epicyclic gear trains are controlled by a hydraulic power circuit that actuates brake bands or multidisk clutches to effect ratio changes, the power circuit being controlled by either a hydraulic or an electronic control circuit responsive to drive torque, to rotary speed of the engine, and/or to the vehicle speed. The drive torque typically is sensed indirectly by detecting the position of the accelerator pedal. The input from the engine to the automatic transmission is accomplished through a hydraulic torque converter, in which the power of the engine is transmitted by a fluid under pressure when the rotary speed of the engine exceeds an idling speed.
In spite of fifty years of improvements, conventional automatic transmissions are still encumbered to some extent by their original disadvantages: great weight, high cost, mediocre efficiency, and poor performance of the vehicle compared with that obtainable with a manually operated gear box.